It may be you haven't heard yet. The notifications are still going out. A very few customers agreed fixed price deals and won't be affected, and some contracts agreed this year are deemed on the new pricing anyway. Most customers are on fixed discount deals, part way through a fixed term and will have had or soon be getting the good news.
You'll find that these days courts and adjudicators will generally accept email and text notification as adequate - few of us sign physical contracts these days and electronically recorded agreements are still enforceable.
Strictly speaking, if they failed to contact you then they can't enforce a price rise, but if the company claim that they wrote, emailed or texted then it can be a challenge to prove otherwise. If it came to this crunch, then you can try taking it to Ombudsman Services.